1. Field of the Invention
The present invention relates to a transmission system having a stand-by line switching facility, the system including therein a plurality of working lines for transferring respective information signals, a stand-by line for replacing a faulty working line and a stand-by line switching apparatus for carrying out the switching between the faulty working line and the stand-by line.
2. Description of the Related Art
A redundant system is usually incorporated in a transmission system so as to increase communication reliability of the transmission system. Namely, if a fault occurs in one of working lines, the faulty working line is bypassed by the redundant system which forms, in usual operation, a stand-by line.
As will be explained hereinafter, the switching from the faulty working line to the stand-by line and vice versa is handled by a switching control unit including therein a central processing unit (CPU). The CPU detects a fault that has occurred in the transmission system and then achieves the switching between the working line and the stand-by line.
In this case, when a fault occurs in the transmission system, the CPU detects the fault and then issues a command to disconnect the faulty working line at a first step. At a second step, the CPU issues another command to connect the stand-by line to the faulty working line to replace the same.
Thus, in the prior art switching operation, at least two commands are to be issued from the CPU. This apparently causes a switching delay, and therefore, rapid switching cannot be expected.